Recently, the network as an information processing infrastructure has been widely spread. Each individual has a mobile terminal such as a mobile telephone and a mobile computer. Thus, data communication between individuals and obtaining various information from information providers (service providers) are performed frequently.
In the society where information is oversupplied, information received by each individual may include unreliable information as well as reliable information. For example, various kinds of information can be written freely in a message box by using the Internet. However, users do not have a device for determining whether or not the information provided from various information sources is reliable. Basically, the users have to determine the reliability at their own risk.
Promiscuous individuals may write information freely in many information supply services using the Internet or the like. The written information includes truly useful information and, conversely, includes useless information and hazardous information. The information amount can be increased because of the widely spread networks, but the processing for extracting useful information therefrom is significantly difficult.